An optical demultiplexer is a device that separates a combined light beam into a plurality of separated light beams. In some instances, the separated light beams have different wavelengths, and in other instances the separated light beams have the same wavelength, but different polarizations. Optical demultiplexers, particularly those that demultiplex optical signals having the same wavelength but different polarizations, are useful in a variety of optical telecommunication equipment, such as optical receivers.